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TPS61183RTJR Datasheet(PDF) 10 Page - Texas Instruments |
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TPS61183RTJR Datasheet(HTML) 10 Page - Texas Instruments |
10 / 25 page 11 SW FSW 5 10 F = R ´ TPS61183 SLVSAB4A – JUNE 2010 – REVISED JULY 2010 www.ti.com DETAILED DESCRIPTION NORMAL OPERATION The TPS61183 is a high efficiency, high output voltage white LED driver for notebook panel backlighting applications. The advantages of white LEDs compared to CCFL backlights are higher power efficiency and lower profile design. Due to the large number of white LEDs required to provide backlighting for medium to large display panels, the LEDs must be arranged in parallel strings of several LEDs in series. Therefore, the backlight driver for battery powered systems is almost always a boost regulator with multiple current sink regulators. For normal operation there must be enough white LEDs in series to ensure the output voltage stays above the input voltage range. Having more white LEDs in series reduces the number of parallel strings and therefore improves overall current matching. However, the efficiency of the boost regulator declines due to the need for high output voltage. The TPS61183 IC has integrated all of the key function blocks to power and control up to 60 white LEDs. The device includes a 40 V / 2.0 A boost regulator, six 30 mA current sink regulators, and a protection circuit for over-current, over-voltage, Open LED, Short LED, and output short circuit failures. The TPS61183 integrates programmable PWM dimming methods with the PWM interface to control output dimming frequency independently with input frequency. An optional direct PWM mode is user selectable through the RFPWM/MODE selection function. SUPPLY VOLTAGE The TPS61183 IC has a built-in linear regulator to supply the IC analog and logic circuit. The VDDIO pin, output of the regulator, is connected to a 1 µF bypass capacitor for the regulator to be controlled in a stable loop. VDDIO does not have high current sourcing capability for external use but it can be tied to the EN pin for start up. BOOST REGULATOR AND PROGRAMMABLE SWITCH FREQUENCY (FSCLT) The fixed-frequency PWM boost converter uses current-mode control and has integrated loop compensation. The internal compensation ensures stable output over the full input and output voltage ranges assuming the recommended inductance and output capacitance values in Equation 1 are used. The output voltage of the boost regulator is automatically set by the IC to minimize voltage drop across the IFB pins. The IC regulates the lowest IFB pin to 350 mV, and constantly adjusts the boost output voltage to account for any changes in LED forward voltages. If the input voltage is higher than the sum of the white LED forward voltage drops (e.g., at low duty cycles), the boost converter is not able to regulate the output due to its minimum duty cycle limitation. In this case, increase the number of WLEDs in series or include series ballast resistors in order to provide enough headroom for the converter to boost the output voltage. Since the TPS61183 integrates a 2.0A/40V power MOSFET, the boost converter can provide up to a 38 V output voltage. The TPS61183 switching frequency can be programmed between 300 kHz to 1.0MHz by the resistor value on the FSW pin according to Equation 1: (1) Where: RFSW = FSW pin resistor See Figure 6 for boost converter switching frequency adjustment resistor RFSW selection. The adjustable switching frequency feature provides the user with the flexibility of choosing the switching frequency. A faster switching frequency will allow for an inductor with smaller inductance and footprint while a slower switching frequency could potentially yield higher efficiency due to lower switching losses. Use Equation 1 or refer to Table 1 to select the correct value: Table 1. RFSW Recommendations RFLCT FSW 833K 600 KHz 625K 800 KHz 499K 1 MHz 10 Submit Documentation Feedback Copyright © 2010, Texas Instruments Incorporated Product Folder Link(s): TPS61183 |
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